Accurate diagnosis of solid pediatric tumors requires a combination of diagnostic techniques including reverse transcription polymerase chain reaction (RT-PCR). Many pediatric solid tumors exhibit fundamental cytogenetic abnormalities that have implications in their pathogenesis. The Ewing's sarcoma family of tumors (ESFT) and alveolar rhabdomyosarcoma (RMS) are characterized by consistent chromosomal translocations which result in the fusion of genes and subsequent formation of novel chimeric genes. These molecular markers can be detected by RT-PCR or fluorescence in situ hybridization (FISH) and can be used not only to establish the diagnosis in difficult cases, but also to understand the pathogenesis of these tumors. Recently, the products of these fusion genes have become the target of vaccine therapies in newly established protocols in the Pediatric Oncology Branch (POB) at the NCI. The objective of this project is: (1) to provide state of the art diagnosis of solid pediatric tumors (2) to assist in the evaluation of pediatric tumor specimens for the presence or absence of specific fusion transcripts and (3) to evaluate the significance of molecular markers in the diagnosis, classification and pathogenesis of pediatric sarcomas. The following accomplishments have been made in the last year: (1) A total of 122 Pathology reports were issued. (2) A total of 51 RT-PCR reports were issued. (3) A series of 72 pediatric sarcomas were evaluated by RT-PCR for the presence or absence of fusion transcripts (Dagher, R. et al Int J Pediatr Hematol Oncol (in press)).(4) Myogenin was established as a rhabdomyosarcoma-specific marker, after evaluation of 119 pediatric tumor cases ( Kumar, S et al. Mod Pathol 2000; 13:988-993).